The effect of soil tillage on the yield and quality of flue-cured tobacco was studied from 1998 to 2001 at the Experimental Station of the Tobacco Institute Zagreb in Croatia. The trial soil was a Luvisol with an acid reaction and a low content of colloids and organic matter. There were three treatments in the experiment: 1. autumn ploughing, 2. spring ploughing, and 3. autumn ploughing + chisel ploughing in spring. The treatments were arranged in random blocks with four replications. Soil ploughed in both autumn and spring gave higher yields of flue-cured tobacco in comparison with autumn ploughing alone. Soil ploughed only in autumn became compacted due to settling during the winter and spring because of the unstable structure and unfavourable texture.

Three field experiments were conducted at the experimental station of the Tobacco Institute Zagreb in Pitomaca during the years 1990 and 1992, 1993-1996 and 1999-2000 to determine the effects of irrigation at different soil moisture levels [40-100%, 60-100%, 80-100% of plant available water, (PAW)], of different starting times of irrigation (vegetative phase, early flowering stage, continuously), and of irrigation combined with nitrogen nutrition (0, 20, 40, 60 kg/ha N) on the yields and quality of flue-cured tobacco. The first two experiments involved block methods, the third involved the split-plot method.In the first experiment, irrigation led to an increase in yield (3-38%), in price/kg (15-69%) and in reducing sugar content (18-89%) and a reduction of nicotine content (20-39%) in the flue-cured leaves. Additional irrigation at the early flowering stage and constant maintenance of soil moisture at a higher level resulted in somewhat lower yields but better visually estimated tobacco quality and, as expected, had a marked influence on the contents of nicotine and reducing sugars.In the second experiment, irrigated tobacco gave higher yields in two of the four trial years, which were significant in 1995 (13-21%), higher reducing sugar levels in 1994 (20-34%) and a marked reduction of nicotine content in cured leaves in all years (11-56%). Under conditions identical with or similar to those used in this research, irrigation may be started at the early flowering stage.In the third experiment, in both years irrigated tobacco showed significantly higher yields, price/kg and reducing sugar levels and significantly lower nicotine content. Averaging the two years indicated increases of 17%, 12% and 26% and a decrease of 29%, respectively. Higher amounts of nitrogen fertilizer promoted yield (up to 32%) and nicotine content (up to 76%), while decreasing reducing sugar levels (by up to 52%). Also, the price/kg of tobacco fertilized with more than 20 kg/ha of nitrogen dropped by as much as 26%.

Investigations of the topping height, ripeness and tobacco variety on the price and quality indices, as expressed by reducing sugars/nicotine, total nitrogen/nicotine and N-proteins/total nitrogen ratios, were conducted during 2004 -2005 and 2007. Trial treatments included: (1) topping height (17 and 20 leaves for harvesting), (2) leaf ripeness at harvest (unripe, ripe and overripe) and (3) variety (HVT 1, VJ 1, DH 17). Investigation results showed that precipitation deficiency in 2004 resulted in a decrease of overripe tobacco prices, while water stress at the intensive growth stage in 2007 caused a significant price increase from unripe to overripe tobacco harvesting. In the first two trial years, the best reducing sugars/nicotine ratios were achieved by overripe tobacco harvesting. In 2007, delayed ripeness of tobacco led to irreparable disruption of the reducing sugars/nicotine ratio, below acceptable limits, irrespective of leaf ripeness at harvest. The total nitrogen/nicotine ratio was within the limits for good-quality tobacco in all trial years, while higher ratios were recorded in the climatically most favourable year 2005 also in tobaccos with higher topping. The N-proteins/ total nitrogen ratio was in the range acceptable for that ratio in ripe tobacco leaves and in overripe tobacco leaves only in the extreme 2007. Significant impact of variety genetic variability on all the studied traits was established. It is also obvious from the results that irreparable impairment of the tobacco leaf chemical quality in 2007 was manifested only in the reducing sugars/nicotine ratio. Strong correlations were found between price and the reducing sugars/nicotine and N-protein/nitrogen ratios and weak correlations with the total nitrogen/nicotine ratio.

Istraživanje je provedeno u 2006. i 2008. kako bi se utvrdio utjecaj visine zalamanja, metode berbe i zrelosti lista u vrijeme berbe na sadržaj ukupnog dušika, bjelančevina, nikotina i reducirajućih šećera. Postupci u pokusu bili su visina zalamanja (17 i 20 listova za berbu), metoda berbe (3, 4 i 7 berbi) i zrelost listova u berbi (nezreli, zreli i prezreli). Primijenjen je split-split plot dizajn s četiri repeticije. Koncentracija istraživanih kemijskih svojstava proučavana je u listovima iz trećeg (6 i 7 list) i sedmog (14 i 15 list) segmenta na stabljici. Visina zalamanja nije utjecala na prosječni sadržaj ukupnog dušika, bjelančevina, nikotina i reducirajućih šećeri. Utjecaj metode berbe na istraživan kemijski sastav bio je mali. Odgađanje berbe uzrokovalo je smanjenja prosječnog sadržaja ukupnog dušika i bjelančevina, povećanja sadržaja nikotina, a sadržaj redukcirajućih šećera povećavao se do optimalne zrelosti ili prezrelosti. Međutim, prisutnost interakcija ukazuje da berba listova duhana u različitim stadijima zrelosti može proizvesti nekonzistentne rezultate ovisno o metodi berbe i visini zalamanja.

Istraživanje s ciljem utvrđivanja utjecaja visine zalamanja (17 i 20 listova za berbu), metode berbe (7, 4 i 3 berbe) i zrelosti (nezreli, zreli i prezreli) na prinos, cijenu i sadržaj nitrata u soku rebra u vrijeme berbe, provedeno je 2006. i 2008. godine. Primijenjen je split-split plot dizajn s čeiri ponavljanja. Viši prinosi u vršnom segmentu ostvareni su višim zalamanjem i obratno u dva niža segmenta. Utjecaj metode berbe na prosječne vrijednosti istraživanih svojstava bio je mali. Zrelost listova u vrijeme berbe u 2006. u pet od šest segmenata nije imala utjecaj na prinos. U 2008. najviši prinosi u vršna tri segmenta ostvareni su berbom zrelih listova. Najviše prosječne cijene u drugom i trećem segmentu ostvarene su berbom zrelih, a u višim segmentima prezrelih listova. Različito zreli listovi u vrijeme berbe u nekim segmentima su proizveli različite rezultate ovisno o visini zalamanja i metodi berbe. Sadržaj nitrata u soku rebra lista u vrijeme berbe kada su postignuti podjednaki ili viši prinosi i cijene opadao je odlaganjem berbe i, uz neke izuzetke, od donjih prema gornjim segmentima. Međutim, na osnovi rezultata ovog istraživanja nije bilo moguće odrediti kritične raspone sadržaja nitrata koji bi se mogli koristiti za procjenu zrelosti listova duhana za berbu.